Pressure sensors and manufacture thereof

ABSTRACT

A pressure sensor comprising a first housing piece defining a lumen therethrough and an opening to said lumen to provide communication between said lumen and a sensing element, said first housing piece having a first surface surrounding said opening, a second housing piece shaped for mating with said first housing piece and providing, with said first housing piece, a region for containing a sensing element in position to communicate with said lumen via said opening, said second housing piece having a second surface that surrounds said region and faces and conforms to the shape of said first surface, said second housing piece including an end of an electrical wire and wire contacts that are electrically connected to said wire, having portions at or near said second surface, and are spaced from each other, a sensing element in said region in communication with said flowpath via said opening, said sensing element including sensor contacts aligned with respective wire contacts, and an elastomeric sheet providing a seal between said first and second surfaces and having a hole therethrough aligned with said opening and plural separate conductors on its surface facing said second surface to make electrical contact between respective said wire contacts and sensor contacts. Also disclosed are insulation displacement blades to provide electrical connection between a sensing element and a wire, and a compressed elastomeric displacement sealing ring filled with gel and providing a communication path between the opening and the sensing element.

This application is a division of application Ser. No. 874,225, filedJune 13, 1986.

FIELD OF THE INVENTION

The invention relates to pressure sensors, e.g., disposable bloodpressure transducers, connected by electrical wires to a monitor.

BACKGROUND OF THE INVENTION

A commercially available disposable blood pressure sensor includes asensing element communicating through an opening in the side of a lumenwhich measures dynamic blood pressure in the cardiovascular system via acatheter and a tubing filled with isotonic fluid. The sensing elementincludes a strain gauge transducer (for example, the type havingresistors ion-implanted in semiconductor material) in which a pressurechange is sensed as a resistance change in a resistor bridge. A monitor,connected to the transducer by a wire permanently connected to thedisposable unit and a reusable cable, supplies two terminals of thebridge with an excitation voltage, and detects an output signal at theother two terminals. The space between the lumen and the transducer isusually filled with a gel so as to transmit pressure without contact ofthe transducer with the blood, thereby providing electrical isolation ofthe patient from the sensing element.

SUMMARY OF THE INVENTION

In one aspect, the invention features a pressure sensor in which a pieceof an elastomeric sheet carrying conductors is used both to provideelectrical connection to a sensing element and to provide a seal betweentwo pieces of the sensor housing, one piece providing a fluid filledlumen and the other piece including the electrical connections betweenthe sensing element and an electrical cable. The use of theconductor-carrying elastomeric sealing sheet advantageously facilitateslow part count and labor and high device integrity, and providesreliable electrical contact without soldering.

In another aspect the invention features a pressure sensor in which anelastomeric displacement sealing ring provides a gel-filledcommunication path between a sensing element and an opening to a lumendefined by a housing, the sealing ring being compressed between thehousing and the sensing element so that the gel fills all voids betweenthe lumen and the sensing element. Manufacture is greatly simplified, asthe gel is easily injected prior to mounting the sensor adjacent to thelumen, and there is no need to employ the time-consuming, difficultprocess of injecting gel from the transducer lumen.

In another aspect, the invention features a pressure sensor in which asensing element in communication with a liquid flow path is connected tomultiple conductors of an electrical wire by using insulationdisplacement blades having sharp ends piercing the insulation of thewire and making electrical contact with the conductors, the sensorhousing providing a liquid tight seal around the insulation displacementblades and the connection portion of the electrical wire. Reliableelectrical connection between the sensor and the wire is provided, andassembly is facilitated, as the displacement blades can be automaticallyhandled by a machine, and processes such as soldering and encapsulationare not required.

In another aspect the invention features in general simplifying theconnection of electrical wire to plastic end pieces, and improving theliquid-tight seal of the plastic end pieces to the electrical wire, bypassing insulated wire through a mold, insert molding pairs of plasticend pieces completely around nearby portions of the wire each time thata predetermined length of wire has passed through the mold, and latercutting the wire between the nearby end pieces to provide individualwires with molded plastic end pieces. This simplifies the prior practiceof first cutting individual wires, and then insert molding the parts tothe ends of the wires, reducing the assembly time and number of partsand avoiding difficult to handle loose individual cables during themanufacturing process. In preferred embodiments, the wire is unwoundfrom a supply reel before molding and wound on a take-up reel aftermolding and prior to cutting the individual wires, permitting thetake-up reel to be brought to the site of further assembly and easilyhandled by a machine; a sensing element is secured to one of the moldedplastic end pieces and electrically connected to multiple conductors ofthe wire; and insulation displacement blades are inserted into themolded plastic end pieces to connect the electrical wire to the sensingelement and provide contacts for mating with a reusable cable of amonitor.

Other advantages and features of the invention will be apparent from thefollowing description of a preferred embodiment thereof and from theclaims.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The drawings will be briefly described first.

Drawings

FIG. 1 is a perspective view of a disposable blood pressure sensoraccording to the invention.

FIG. 2 is a partial elevation, partly in section, of the FIG. 1 sensor.

FIG. 3 is an exploded perspective view of a conductor-carryingelastomeric sheet, an elastomeric displacement sealing ring and asensing element of the FIG. 1 sensor.

FIG. 4 is a schematic of the manufacturing process for the molded endpieces of the FIG. 1 sensor.

FIG. 4a is an elevation of part of the wire carrying a pair of nearbyplastic end pieces during the manufacturing process shown in FIG. 4.

FIG. 5 is a perspective view showing a two-piece connection assemblyincluding an electrical connector of the FIG. 1 sensor and a connectorof a reusable cable attached to a monitor.

FIG. 6 is an elevation, partially broken away, showing the FIG. 5connectors connected together.

FIG. 7 is a perspective view of a component of the FIG. 5 connectorattached to the reusable cable prior to final assembly.

FIG. 8 is a side elevation, partially broken away, of the FIG. 7component.

FIG. 9 is a bottom plan view of the FIG. 7 component.

FIG. 10 is a elevation showing a heat shrinkable tube and insertedcontact and wire of the FIG. 7 component prior to heat shrinking.

STRUCTURE

Referring to FIG. 1, there is shown disposable blood sensor 10 includingsensing unit 12 with threaded ends 14 for connection to a fluid filledtube connected to the cardiovascular system via a catheter via lindennuts (all three not shown), and pigtail multiconductor electrical wire16 and electrical connector 18.

Referring to FIG. 2, it is seen that sensing unit 12 includes clearplastic housing 20 defining fluid path 22 having opening 24 between itand cavity 40 inside of the lower portion of clear plastic housing 20.Plastic molded end piece 26 is mounted in cavity 40. End piece 26 ismolded around the end of wire 16 by the process shown in FIG. 4. Wire 16is unwound from supply reel 28, and connecting end piece 26 and plastichousing 30 of connector 18 are simultaneously molded around nearbyportions of wire 16 at molder 32 prior to rewinding on take-up reel 34.Wire 16 is advanced by slightly more than the desired length between endpiece 26 and housing 30 between each molding step. In a furthermanufacturing step, the individual pieces of wire 16 with connecting endpiece 26 and housing 30 on respective ends are provided by slicing wire16 at the small pieces 36 of wire 16 between nearby pairs of end pieces26 and housings 30, removing pieces 36 and sealing off exposedconductors.

Referring to FIGS. 2 and 3 four insulation displacement blades 37 areinserted in molded channels in the upper surface of end piece 26. Blades37 have sharp pointed ends 39 that pierce insulation 41 coveringconductors 43 making electrical contact with them. Blades 37 are made of0.014" thick phosphor bronze, spring tempered, and provided with hardgold plate over nickel. Manufactured in continuous strips, they areeasily automatically handled by an insertion machine.

Sandwiched between upper surface 35 of molded end piece 26 and the lowersurface 38 at the top of cavity 40 of housing 20 is elastomeric sheet 42carrying metalization 44 on its lower surface. Provided in upward-facingrecess 46 of end piece 26 are lid 48, semiconductor strain gaugetransducer 50, adhesive sealing ring 52 around the periphery oftransducer 50 and above it, ceramic substrate 54 carrying conductivepaths 56, and elastomeric displacement sealing O-ring 58. Displacementsealing ring 58 is sufficiently compressed so as to reduce its interiorvolume by an amount to cause displacement of gel so as to occupy allspace between it and opening 24, as is discussed below. Metallization 44may include for example a plurality of fine separate parallel lines 45extending longitudinally on sheet 42 for making electrical contactbetween blades 37 and respective conductive paths 56. Sheet 42 is madeof material such as silicone, and metal lines 45, in the preferredembodiment, are each 5 mils wide and spaced from adjacent lines by 5mils and are made of copper coated with nickel and gold. On the lowersurface of semiconductive transducer 50 is a layer of isolation gel (notshown) within recess 60 of lid 48.

In manufacture, semiconductor transducer 50 is adhered to the bottom ofceramic substrate 54 by adhesive 52; electrical wires (not shown) areadded to electrically connect transducer 50 to substrate 54; theisolation gel is applied to the lower surface of transducer 50, and lid48 is adhered to the lower surface of ceramic substrate 54. Theassembled unit including lid 48, transducer 50 and substrate 54 arecollectively referred to herein as sensing element 59, as indicated onFIG. 3. Displacement sealing ring 58 is adhesively adhered to the uppersurface of the ceramic substrate 54, and isolation gel 62 is injectedinto opening 64 of ring 58 and passes down through hole 66 of substrate54 and into the region between the lower surface of substrate 54 and theupper surface of transducer 50, filling all voids within sensing element59 and ring 58. Sensing element 59 and attached ring 58 are placed inrecess 46 of end piece 26, which is inserted in cavity 40 of housing 20with elastomeric sheet 42 between surface 38 of housing 20 and facingsurface 35. Prior to staking end piece 26 to housing 20, displacementsealing ring 58 is compressed, causing gel 62 therein to rise upwardinto opening 24. Elastomeric sheet 42 is similarly compressed prior tostaking, providing a liquid tight seal between surface 38 surroundingopening 24 and upper surface 35 of plastic end piece 26. Sealing ring 58similarly provides a liquid tight seal between opening 24 and theexposed upper surface of sensing element 59, providing a communicationpath between the two for communicating pressure. Lid 48 includes ventinghole 70 which communicates with channel 72 in the center bottom ofrecess 46, in turn communicating with hole 74 provided to the centerchannel 76 of wire 16 from which the conductor has been removed toprovide venting to the space within recess 60 of lid 48.

Referring to FIGS. 5-6, connector 18 of disposable blood sensor 10 isshown in position for mating with connector 78 of reusable cable 80,connected to a monitor (not shown). Connector 18 includes fourinsulation displacement blades 82 in insertion end 84 (FIGS. 1, 6).Blades 82 have sharp pointed ends piercing the insulation of wire 16 andmaking electrical connection with respective conductors 43 in housing30. Connector 78 includes locking and sealing ring 86 that is rotatablymounted on end tube 88 and retained by lip 90 on ring 86 and tabs 92 onend tube 88. Ring 86 includes two tabs 94 that mate with cammingsurfaces 96 of connector 18.

Referring to FIGS. 7-9, it is seen that inside of end tube 88 is plasticcontact support 98 including grooves 100 in the flat surface ofextension 102 and grooves 104 in the face of surface 106 perpendicularto the flat surface of extension 102. Resilient contact members 108(gold plated phosphor bronze wires, about 18 mils in diameter, forexample) extend from grooves 100 at the end of extension 102 to grooves104, and have free ends in grooves 104, permitting resilient pivotingabout the end of extension 102. Referring to FIGS. 8 and 9, it is seenthat midsections 110 of contacts 108 pass through spaced channels inbase 112 of support 98 in which they are retained. Referring to FIGS. 9and 10, connection ends 114 of contacts 108 are within heat shrunkplastic tubes 116 having solder sleeves 118 therein. Tubes 116 extend upto base 112, where midsections 110 of the contacts are spaced from eachother, owing to mounting in separate channels of base 112. Ends 114 areconnected to electrical wires 120, the ends of which are also in heatshrunk tubes 116. As can best be seen in FIG. 9, contacts 108 arealigned in close proximity with each other and are connected to aplurality of non-aligned overlapping wires 120 in cable 80. Heat shrunktubes 116 permit the connection between the two without the use ofstaggering of connections, contributing to the small overall size ofconnector 78. In manufacture, after the contacts have been mounted insupport 98 and connected to wires 120, clip 122 is provided, as shown inFIGS. 7-9; end tube 88, carrying locking ring 86, is then slid overextension 102 and up against lip 124, and outside plastic cover 126 ismolded around the entire assembly.

OPERATION

In use, ends 14 of disposable sensor 10 are secured to an isotonic fluidfilled tube using linden nuts. Pressure signals from the patient'svascular system communicate its pressure to gel 62 in opening 24, whichin turn communicates it to the upper surface of semiconductor straingauge 50, and the pressure is determined by electrical signals receivedby the monitor (not shown). Electrical connection from ceramic substrate54 to wire 16 is provided by the parallel conductor lines 45 on thebottom of elastomer sheet 42, and insulation displacement blades 37.

Locking ring 86 provides a liquid resistant seal and positive lockingbetween connectors 18, 78. Elastomer sheet 42 provides a liquid tightseal within sensing unit 12.

OTHER EMBODIMENTS

Other embodiments of the invention are within the scope of the followingclaims. For example, instead of a large number of thin metal lines 45,four discrete conductors, aligned with blades 37 and conductive paths56, could be used to provide electrical connection between the two.

What is claimed is:
 1. A pressure sensor comprisinga housing defining alumen therethrough and an opening to said lumen to provide communicationbetween said lumen and a sensing element, said opening passing through awall of said housing from a surface on the other side of said wall fromsaid lumen to said lumen, said opening being smaller in area than saidlumen, a sensing element, a support for mounting said sensing element inposition for communication with said opening, an elastomericdisplacement sealing ring between said housing and said sensing element,said ring contacting said surface around said opening and providing acommunication path between said opening and said sensing element, saidring being made of compressible material, and a gel inside said sealingring and occupying space between said communication path and saidsensing element, said gel being injected into said sealing ring prior tomounting said sensing element for communication with said opening, saidring being sufficiently compressed so as to reduce its interior volumeby an amount to cause displacement of gel so as to occupy all spacebetween said ring and said opening and to occupy space in said opening.